Stainless Steel Coil Tube (Coiltube) — Product Technical Specification
1. Product Overview
The Stainless Steel Coil Tube (Coiltube) manufactured by Wenzhou Jixing Metal Materials Co., Ltd. is a precision-engineered, continuously wound tubular component designed for fluid transport, heat exchange, and pressure containment applications. As a critical element in low-temperature heating systems, HVAC (Heating, Ventilation, and Air Conditioning) installations, and industrial process piping, the coil tube offers superior thermal conductivity, corrosion resistance, and mechanical integrity compared to conventional carbon steel alternatives.
Based on extensive research into the heating performance of radiators and fan coil units (FCU) within low-temperature heating systems, this product has been optimized to maximize heat transfer efficiency while maintaining structural reliability under cyclic thermal loading. The coil configuration provides a high surface-area-to-volume ratio, enabling rapid thermal response and uniform heat distribution across connected radiators or fan coil units.
2. Material & Properties
2.1 Base Material
- Primary Alloy: Austenitic Stainless Steel — Grade 304 (UNS S30408) and Grade 316L (UNS S31603)
- Composition (Grade 304): Chromium (Cr) 18–20%, Nickel (Ni) 8–10.5%, Manganese (Mn) ≤2%, Carbon (C) ≤0.08%
- Composition (Grade 316L): Chromium (Cr) 17–18%, Nickel (Ni) 10–14%, Molybdenum (Mo) 2–3%, Carbon (C) ≤0.03%
2.2 Mechanical Properties
| Property | Grade 304 | Grade 316L |
|---|---|---|
| Tensile Strength (MPa) | ≥520 | ≥485 |
| Yield Strength (MPa) | ≥205 | ≥170 |
| Elongation (%) | ≥40 | ≥40 |
| Hardness (HB) | ≤200 | ≤200 |
| Thermal Conductivity (W/m·K, at 100°C) | 16.3 | 14.6 |
| Maximum Operating Temperature (°C) | 870 | 870 |
| Corrosion Resistance (Pitting Resistance Number) | 18–20 | 24–26 |
2.3 Surface Treatment
- Standard Finish: 2B Cold-Rolled Annealed Finish (Ra ≤ 0.8 μm)
- Available Finishes: No. 4 Brushed, 8K Mirror, BA (Bright Annealed) for vacuum applications
- Passivation: Citric acid passivation per ASTM A967 to enhance passive oxide layer stability
3. Specifications
| Parameter | Specification |
|---|---|
| Outer Diameter (OD) | 6 mm – 51 mm (custom sizes available) |
| Wall Thickness (WT) | 0.5 mm – 4.0 mm |
| Coil Winding Diameter | 100 mm – 500 mm |
| Coil Length (per bundle) | 3 m – 30 m (configurable) |
| Winding Pitch | 1.1 × OD to 2.0 × OD |
| Helix Angle (Deviation from 90°) | ≤ 1.5° |
| Roundness Tolerance | ≤ 2% of OD |
| Wall Thickness Tolerance | ±10% of nominal |
| Working Pressure (PN) | PN6 – PN16 (up to 1.6 MPa) |
| Pressure Test | 1.5× working pressure, held for ≥5 minutes |
| Applicable Standards | ASTM A213, ASTM A269, EN 10217-7, GB/T 12771 |
4. Manufacturing Process
- Strip Selection & Inspection: Cold-rolled stainless steel strip is sourced from certified mills and subjected to chemical composition analysis (OES spectroscopy) and mechanical property verification.
- Pipe Forming (Seamless or Welded): The strip is formed into tubular shape via roll-forming or hydraulic expansion. For welded coils, TIG (Tungsten Inert Gas) welding or laser welding is employed with argon gas shielding (minimum 99.99% purity) to prevent intergranular corrosion.
- Heat Treatment: Solution annealing at 1050–1150°C followed by controlled water quenching to dissolve carbides and restore full austenitic microstructure, ensuring optimal corrosion resistance.
- Coil Winding: The formed tube is precisely wound onto a mandrel using CNC-controlled coiling machines. Winding parameters (pitch, helix angle, tension) are programmed to ensure uniform spacing and eliminate inter-turn contact stress.
- End Finishing: Tube ends are deburred, chamfered, and optionally threaded or equipped with compression fittings for seamless system integration.
- Quality Inspection: 100% visual inspection, dimensional verification via calipers and micrometers, hydrostatic pressure testing, and optional Eddy Current (EC) testing for weld seam integrity.
5. Applications
5.1 Low-Temperature Heating Systems
As demonstrated in research on radiator and fan coil unit (FCU) heating performance in low-temperature systems, the coil tube serves as the primary heat exchange element. Its high surface-area-to-volume ratio enables efficient convective and radiative heat transfer, reducing the required supply water temperature while maintaining adequate thermal output — a key advantage for energy-efficient heating design.
5.2 Industrial Applications
- HVAC Systems: Air handling units, fan coil units, and condenser coils
- Food & Beverage Industry: Heat exchangers, pasteurization equipment, brewing systems (FDA-compliant)
- Chemical Processing: Reactor cooling coils, distillation column internals, corrosive fluid transport
- Pharmaceutical: Cleanroom piping, sanitary heat exchange (EHEDG-compliant)
- Marine & Offshore: Seawater cooling circuits, ballast water systems (Grade 316L)
- Renewable Energy: Solar thermal collector manifolds, geothermal loop systems
6. Quality Certifications & Compliance
| Certification / Standard | Description |
|---|---|
| ISO 9001:2015 | Quality Management System certification |
| ISO 14001:2015 | Environmental Management System certification |
| CE Marking | Compliance with EU Pressure Equipment Directive (PED 2014/68/EU) |
| EN 10204 3.1 | Material test certificate per European standard |
| NSF/ANSI 61 | Drinking water system components (available upon request) |
| GB/T 12771 | Chinese national standard for welded stainless steel tubes |
7. Unique Selling Points
- Enhanced Thermal Performance: Optimized coil geometry based on empirical data from low-temperature heating system studies, achieving up to 15% higher heat transfer coefficient compared to standard spiral coils.
- Corrosion Immunity: Full austenitic microstructure provides resistance to pitting, crevice corrosion, and stress corrosion cracking (SCC) even in aggressive environments containing chlorides.
- Precision Manufacturing: CNC-controlled coiling ensures dimensional accuracy within ±0.1 mm, critical for heat exchanger tube-sheet insertion and system integration.
- Sanitary Grade Available: BA finish with electropolished interior (Ra ≤ 0.4 μm) suitable for pharmaceutical and food-grade applications.
- Custom Configuration: Flexible design parameters (OD, WT, coil diameter, pitch, length) to meet project-specific thermal and hydraulic requirements.
- Full Traceability: Each coil batch is accompanied by a mill test certificate (MTC) with heat number, chemical analysis, and mechanical test results.
8. Technical Notes
Design Consideration: In low-temperature heating systems operating with supply water temperatures below 40°C, the stainless steel coil tube maintains superior thermal conductivity relative to carbon steel alternatives, reducing system pressure drop while delivering consistent radiative output. The material's resistance to dezincification and general corrosion ensures a service life exceeding 25 years in potable water and heating loop applications without replacement.